Remove unneeded __init__. (#15926)

Remove an __init__ which only calls super() without changing the
input arguments.

changelog.d/15926.misc

@@ -0,0 +1 @@
+Remove unneeded `__init__`.

synapse/federation/transport/server/federation.py

@@ -432,15 +432,6 @@ class FederationV2SendJoinServlet(BaseFederationServerServlet):
 
     PREFIX = FEDERATION_V2_PREFIX
 
-    def __init__(
-        self,
-        hs: "HomeServer",
-        authenticator: Authenticator,
-        ratelimiter: FederationRateLimiter,
-        server_name: str,
-    ):
-        super().__init__(hs, authenticator, ratelimiter, server_name)
-
     async def on_PUT(
         self,
         origin: str,